Handle private docker registry auth

This adds support for private docker registries, by adding
an optional `registryAuth` field in the CreateFunctionRequest.
Auth must be passed as base64-encoded basic auth, similar to
how done in Docker file store credentials (~/.docker/config.json).
Credentials are then passed to swarm at service creation.

gateway/tests/registryauth_test.go

@@ -0,0 +1,73 @@
+// Copyright (c) Alex Ellis 2017. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+package tests
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"github.com/alexellis/faas/gateway/handlers"
+	"github.com/docker/docker/api/types"
+)
+
+func TestBuildEncodedAuthConfig(t *testing.T) {
+	// custom repository with valid data
+	assertValidEncodedAuthConfig(t, "user", "password", "my.repository.com/user/imagename", "my.repository.com")
+	assertValidEncodedAuthConfig(t, "user", "weird:password:", "my.repository.com/user/imagename", "my.repository.com")
+	assertValidEncodedAuthConfig(t, "userWithNoPassword", "", "my.repository.com/user/imagename", "my.repository.com")
+	assertValidEncodedAuthConfig(t, "", "", "my.repository.com/user/imagename", "my.repository.com")
+
+	// docker hub default repository
+	assertValidEncodedAuthConfig(t, "user", "password", "user/imagename", "docker.io")
+	assertValidEncodedAuthConfig(t, "", "", "user/imagename", "docker.io")
+
+	// invalid base64 basic auth
+	assertEncodedAuthError(t, "invalidBasicAuth", "my.repository.com/user/imagename")
+
+	// invalid docker image name
+	assertEncodedAuthError(t, b64BasicAuth("user", "password"), "")
+	assertEncodedAuthError(t, b64BasicAuth("user", "password"), "invalid name")
+}
+
+func assertValidEncodedAuthConfig(t *testing.T, user, password, imageName, expectedRegistryHost string) {
+	encodedAuthConfig, err := handlers.BuildEncodedAuthConfig(b64BasicAuth(user, password), imageName)
+	if err != nil {
+		t.Log("Unexpected error while building auth config with correct values")
+		t.Fail()
+	}
+
+	authConfig := &types.AuthConfig{}
+	authJSON := base64.NewDecoder(base64.URLEncoding, strings.NewReader(encodedAuthConfig))
+	if err := json.NewDecoder(authJSON).Decode(authConfig); err != nil {
+		t.Log("Invalid encoded auth", err)
+		t.Fail()
+	}
+
+	if user != authConfig.Username {
+		t.Log("Auth config username mismatch", user, authConfig.Username)
+		t.Fail()
+	}
+	if password != authConfig.Password {
+		t.Log("Auth config password mismatch", password, authConfig.Password)
+		t.Fail()
+	}
+	if expectedRegistryHost != authConfig.ServerAddress {
+		t.Log("Auth config registry server address mismatch", expectedRegistryHost, authConfig.ServerAddress)
+		t.Fail()
+	}
+}
+
+func assertEncodedAuthError(t *testing.T, b64BasicAuth, imageName string) {
+	_, err := handlers.BuildEncodedAuthConfig(b64BasicAuth, imageName)
+	if err == nil {
+		t.Log("Expected an error to be returned")
+		t.Fail()
+	}
+}
+
+func b64BasicAuth(user, password string) string {
+	return base64.StdEncoding.EncodeToString([]byte(user + ":" + password))
+}